Disorders of mineral metabolism have been evaluated with methods extending from epidemiology to cellular biology. Two forms of familial hyperparathyroidism have been characterized in detail. Familial hypocalciuric hypercalcemia is an autosomal dominant trait associated with abnormal interactions with calcium in parathyroid and kidney. Familial multiple endocrine neoplasia type 1 is an autosomal dominant trait causing hyperfunction of parathyroids, pancreatic iseit and anterior pituitary. It is associated with gradual but abnormal proliferation of the tissues affected. Genetic linkage studies in a large kindred have localized the MEN1 gene to the long arm of chromosome 11. Plasma from affected persons shows high mitogenic activity upon cultured bovine parathyroid cells. This mitogenic activity in plasma may be detectable early in life and may be the cause of primary hyperparathyroidism in familial multiple endocrine neoplasia type 1.